Hitherto, active carbon such as granular carbon, powdery carbon, pulverized carbon, etc., has been widely utilized as a material for removing impurities, toxic materials, bad smells, etc., in gases or liquids. Recently, active carbon fibers (hereinafter, also referred to as ACF; ACF is also sometimes called fibrous active carbon) have been developed and used for the same purposes as active carbon. Since ACF has features in the form different from granular active carbon, etc., has a high adsorption rate and gives less formation of fine powders, the use thereof is being expanded rapidly.
ACF derived from acrylic fibers and having high adsorptive characters has been developed (see, Japanese Patent Publication No. 1803/84 and Japanese Patent Application (OPI) Nos. 71,614/'80 (the term "OPI" indicates an unexamined published patent application open to public inspection), Japanese Patent Application (OPI) No 130110/'83 (which corresponds to U.S. Pat. No. 4,460,650); and U.S. Pat. Nos. 4,256,607; 4,285,831; 4,362,646; 4,412,937, etc.). ACF have a specific surface area of about from 500 to 2,000 m.sup.2 /g and a ratio of a pore volume (Vp) to specific area (SA) of from 3.5.times.10.sup.-4 to 7.5.times.10.sup.-4, and shows a very high adsorption character for low molecular weight compounds having molecular weights lower than about 120 and compounds having a small molecular volume in the vapor-phase or the liquid-phase, in particular the vapor-phase use.
However, in the case of using for water purification, conventional ACF cannot sufficiently attain the desired purposes even if ACF derived from acrylic fiber by a conventional method are used. That is, in the case of water purification, a waste liquid to be treated sometimes contains various materials from low molecular weight compounds to high molecular weight compounds but conventional ACF have small pore diameters and hence cannot adsorb high molecular weight compounds having molecular weights of higher than about 500. That is, conventional ACF cannot inclusively remove by adsorption various compounds having a wide range of molecular weights.